Photoconductive copolymer of N-vinylcarbazole and N-vinylphthalimide

ABSTRACT

Polymeric compositions comprising the product of the addition polymerization of N-vinylcarbazole and at least one member selected from the group consisting of N-vinylphthalimide and the isostructural modifications thereof. Many of the above polymeric products are photoconductive and, thus, are suitable for use in electrophotography.

United States Patent Limburg et a1.

PHOTOCONDUCTIVE COPOLYMER 0F N-VINYLCARBAZOLE AND N-VINYLPHTHALIMIDEInventors: William W. Limburg, Penfield;

Donald A. Seanor, Pittsford, both of N.Y.

Xerox Corporation, Stamford, Conn.

Filed: Mar. 19, 1973 App]. No.: 342,646

Assignee:

US. Cl 96/l.5; 260/78.4 D; 260/803 R;

Int. Cl G03g 5/06 Field of Search 96/15, 1.6; 260/78.4 D, 260/803 R,88.3 R, 78.5 T

References Cited UNITED STATES PATENTS 1/1963 Angelo 96/15 X PrimaryExaminer-Roland E. Martin, Jr. Attorney, Agent, or Firm-James J.Ralabate; James P. OSullivan; John H. Faro [57] ABSTRACT Polymericcompositions comprising the product of the addition polymerization ofN-vinylcarbazole and at least one member selected from the groupconsisting of N-vinylphthalimide and the isostructural modificationsthereof. Many of the above polymeric products are photoconductive and,thus, are suitable for use in electrophotography.

15 Claims, 3 Drawing Figures PATENIEBAFR I 51915 3,877. 936

sum 1 i 3 LOG (PHOTOCURRENT) (AMPS) +VE POTENTIAL 1. I00%POLYVINYLCARBAZOLE 2. 50/50 N -VINYLCARBAZOLE/N-VINYLPHT HALIMIDE 3.75/25 N-VINYLCARBAZOLE/N-VINYLPHTHALIHIDE l I I WAVELENGTH (A) INUDENTPHOTON FLUX 1A x 10" PHOTONS/cm AT #7003 ACTION SPECTRA NORMALIZED TOEQUAL INCIDENT PHOTONS FILM THICKNESS: H AREA 1.7cm

SEMITRANSPARENT CHROMIUM ELEURODES PJJENTEB 3,877. 936

' sum 2 {If 3 LOG (PHOTOCURRENT) (AMPS) E l l I 2000 3000 I000 $000WAVELENGTH (A) -VE POTENTIAL I. 100% POLYVINYLCARBAZOLE 2. 50/50-N-VINYLCARBAZOLE/N-VINYLPHTHALIMIDE 3 75/25N-VINYLC'ARBAZOLE/N-VINYLPHTHAUNIDE O mcmavr PHOTON FLUX. m x 10"PHOTONS/cm AT 0700A ACTIQN SPECTRA NORMAL/ZED TO EQUAL uvcmszvr PHOTONSFILM THICKNESS. w, ,AREA 1.7m

SEMITRANSPA RENT CHROMIUM ELECTRODES ATENTEB 1 51975 3. 877. 936

sum 3 o 3 A/b (cm U A(nm) HOMOPOLYMER MIXTURE (50 nousPOLY(N-VINYLCARBAZOLE) +50 HOLE poum-vmmmmumosn (OPOLYHER or THISmvsnnou FIG.3 (50:50 MOLE 9.; N-WNYLPHTHALIMIDE/N-l/INYLCARBAZOLE)PHOTOCONDUCTIVE COPOLYMER ()F N-VINYLCARBAZOLE AND N-VlNYLPHTHALlMlDEBACKGROUND OF THE INVENTION 1. Field of thc lnvention This inventionrelates to polymeric compositions and the use of many of thesecompositions in electrophotographic elements and processes. Morespecifically, this invention involves random copolymers, many of whichare photoconductive and. thus, suitable for use in electrophotographicimaging members and processes. The spacial constraint and relativeconformation of the functional groups of the two principal components ofthese compositions apparently favors a charge transfer interactionbetween them.

2. Description of the Prior Art The formation and development of imageson the imaging surfaces of photoconductive materials by electrostaticmeans is well known. The best known of the commercial processes, morecommonly known as xerography, involves forming a latent electrostaticimage on an imaging surface of an imaging member by first uniformlyelectrostatically charging the surface of the imaging layer in the darkand then exposing this electrostatically charged surface to a light andshadow image. The light struck areas of the imaging layer are thusrendered conductive and the electrostatic charge selectively dissipatedin these irradiated areas. After the photoconductor is exposed, thelatent electrostatic image on this image bearing surface is renderedvisible by development with a finely divided colored electroscopicmaterial, known in the art as toner. This toner will be principallyattracted to those areas on the image bearing surface which retain theelectrostatic charge and thus form a visible powder image.

The developed image can then be read or permanently affixed to thephotoconductor where the imaging layer is not to be reused. This latterpractice is usually followed with respect to the binder-typephotoconductive films (e.g. ZnO) where the photoconductive imaging layeris also an integral part of the finished copy.

1n so-called plain paper" copying systems, the latent image can bedeveloped on the imaging surface of a reusable photoconductor ortransferred to another surface, such as a sheet of paper, and thereafterdeveloped. When the latent image is developed on the imaging surface ofa reusable, photoconductor, it is subsequently transferred to anothersubstrate and then permanently affixed thereto. Any one of a variety ofwell known techniques can be used to permanently affix the toner imageto the copy sheet, including overcoating with transparent films, andsolvent or thermal fusion of the toner particles to the supportivesubstrate.

In the above plain paper" copying system, the materials used in thephotoconductive layer should preferably be capable of rapid switchingfrom insulative to conductive to insulative state in order to permitcyclic use of the imaging surface. The failure of a material to returnto its relatively insulative state prior to the succeeding chargingsequence will result in an increase in the dark decay rate of thephotoconductor. This phenomenon, commonly referred to in the art asfatigue, has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of thematerials suitable for use in such a rapidly cycling system includeanthracene, sulfur. selenium and mixtures thereof (U.S. Pat. No.2,297,691); selenium being preferred because of its superiorphotosensitivity.

ln addition to anthracene, other organic photoconductive materials, mostnotably. poly(N- vinylcarbazole), have been the focus of increasinginterest in electrophotography. Most organic photoconductive materials,including poly(N-vinylcarbazole), lack the inherent photosensitivity tobe competitive with selenium. This need for the enhancement of thephotoresponse characteristics or organic photoconductors thus led to theformulation of these organic materials with other compounds, commonlyreferred to as activators." poly( vinylcarbazoles), for example, whensensitized with 2,4,7-trinitro-9-fluorenone exhibit good photoresponseand discharge characteristics and, (depending upon the polarity of thesurface charge), low dark decay; U.S. Pat. No. 3,484,237. Other organicresins, traditionally considered nonphotoconductive can also besensitized with certain activators, such as Lewis Acids, thus formingcharge transfer complexes which are photoresponsive in the visible bandof the spectrum, U.S. Pat. Nos. 3,408,181; 3,408,182; 3,408,183;3,408,184; 3,408,185; 3,408,186; 3,408,187; 3,408,188; 3,408,189; and3,408,190. With respect to both the photoconductive andnonphotoconductive resins, the degree of sensitization is generallyconcentration dependent; the higher the loadings of activators; thegreater the photoresponse.

The concentration of activator capable of formulation with the abovematerials, however, is finite; generally being limited to less than 10weight percent of the composition. Ordinarily, the addition of highloadings of activator to many of the above materials will lead toimpairment of mechanical and/or the photoconductive properties of thesensitized composition. In most instances, the excessive addition ofactivators to both the photoconductive and nonphotoconductive materialsof the types disclosed in the above patents will result incrystallization of these activators, thus impairing the mechanicalstrength and other physical properties of the resultant photoconductivecomposition. Still yet other sensitizers, when present in relatively lowconcentration can result in over sensitization of the composition inthat the photocurrent generated upon exposure will persist long afterillumination ceases, BUL. CHEM. SOC. of .lAP. 39: 1660 1670 (1966). Thisphenomenon prevents the further use of such materials for preparation ofsuccessive electrostatic reproductions until such presistentconductivity is dissipated in the previously illuminated areas of thephotoconductor. The dissipation of persistent photocurrents generallytakes an extended period of time and/or thermal erasure, thus makingthese oversensitized compositions generally unsatisfactory for rapidcycling electrostatographic imaging systems.

As an alternative to the more traditional type of sensitizationdiscussed above, lnami and Morimoto have proposed preparation of*intramolecular" charge transfer complexes wherein the electron donorand electron acceptor functions are located along a common vinylbackbone, U.S. Pat. No. 3,418,116. The materials of principal interestdisclosed in the above patent are the nitrated vinyl polymers ofpolyacenaphthylene, poly-9-viny1carbazole and poly-1- vinylnaphthalene.More recently, Podhajny has proposed his own intramoleculaf type chargetransfer complex system wherein the electron donor and electron acceptorfunctions are contributed by 3,6-diphenyl-vinylcarbazole and3,6-dinitrm'inylcarbazole. respectively; US. Pat. No. 3,697,264. A morein depth treatment of this type of charge transfer complex system isoffered by Breen and Keller, J. Am. Chem. Soc. 90. 1935, (1968). It isthought that the spacial constraint placed upon the electron donor andelectron acceptor functions enhances the probability of charge transferinteraction. In addition, certain conformational and steric requirementsmust also be satisfied in order to facilitate efficient overlap of donorand acceptor electron orbitals required of this type of charge transferinteraction.

It is, thus, the object of this invention to provide polymericcompositions wherein the structural units thereof are from at least twovinyl monomers, one having an electron donor and a second having andelectron acceptor function. More specifically, the principal object ofthis invention is to provide a photoconductive composition having anelectron donor and an electron acceptor function.

It is another object of this invention to provide a photoconductivecomposition wherein the electron donor and electron acceptor functionsare arranged along a common polymeric backbone.

It is yet another object of this invention to provide a photoconductivecomposition wherein the electron donor and electron acceptor functionsare arranged along a common polymeric backbone in such a fashion as tofavor intramo1ecular" charge transfer complex formation.

SUMMARY OF THE INVENTION The above and related objects are achieved byproviding a polymeric composition comprising structural units from (i)N-vinylcarbazole and (ii) at least one member selected from the groupconsisting of N- vinylphthalimide and the isostructural modificationsthereof. Since the principal area of proposed utility of the abovecomposition resides in the electrophotographic arts, the preferredcompositions are photoconductive; the carbazole moiety providing theelectron donor function and the phthalimide moiety providing theelectron acceptor function. These preferred copolymers will generallycontain from about 50-90 mole percent structural units fromN-vinylcarbazole and from about to about 50 mole percent structuralunits from N-vinylphthalimide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphic illustration ofthe log of photocurrent vs. wavelength applied light for two of thecopolymers of this invention and poly-N-vinylcarbazole. In eachinstance, the photoresponse was measured under an applied positivepotential.

FIG. 2 is a similar graphical illustration of photocurrent vs.wavelength for these same compositions when under an applied negativepotential.

FIG. 3 is a graphical illustration of the charge transfer band of thepreferred photoconductive composition of this invention.

DESCRIPTION OF THE INVENTION Preliminary to preparation of the randomcopo1y mers of this invention, the vinyl monomers should preferably bepurged of impurities. With respect to N- vinylcarbazole, this isachieved by vacuum sublimation, or by recrystallization of this monomerfrom methanol under nonoxidizing conditions. The N- vinylphthalimidemonomer can be purified by passing a benzene solution thereof through aWoelm neutral aluminua column, followed by recrystallization frombenzene. Subsequent to recovery of the above purified monomers they canbe formed into the polymeric compositions of this invention by standardfree radical initiated addition polymerization techniques. It isgenerally preferred that the above monomers be reacted with one anotherunder conditions which favor formation of copolymers havingsubstantially the same mole ratio with respect to its structural unitsas the concentration of monomers in the charge.

In a representative embodiment of this invention, a copolymer containingabout 9 mole percent structural units from N-vinylphthalimide and about91 mole percent structural units from N-vinylcarbazole can be preparedaccording to the following procedure. About 0.866 grams (0.005 moles) ofN-vinylphthalimide and 9.16 grams (0.05 moles) of N-vinylcarbazole aredissolved in 25 milliliters anhydrous benzene. The monomer solution isthen transferred to a 50 milliliter polymer tube. A free radicalinitiator, such as azobisisobutyronitrile, is then introduced into thesolution. Generally about 0.03 grams (1.8 X 10- 4 moles) initiator isadequate to facilitate substantially complete copolymerization of thetwo monomeric materials. After addition of the initiator, the monomersolution is degassed three times by conventional freeze-thaw methods andthen the tube sealed under a vacuum. The sealed polymer tube is thenplaced in a constant temperature bath at 75C and allowed to remain therefor about 12 hours. During this interval, the contents of the tubedevelop a yellowish color. The tube is then removed from the constanttemperature bath, cooled, the seal broken and the polymeric productseparated from the reaction medium by precipitation with hexane. Thisprecipitation is generally carried out by continuous agitation of thehexane-polymer slurry ina Waring blender. Once separated, the crudepolymeric product is purified by redissolving it in a minimum amount ofa mixture of benzene/tetrahydrofuran 1:2 by volume) and thenreprecipitated from hexane. The recovered polymeric solids are thenredissolved and precipitated as described above three additional times.The polymer solids thus produced have a pale yellow tint and display ayellow-green fluorescence when observed under ultraviolet light. Priorto further analysis, the polymer solids are dried overnight in a vacuumoven at about C. Further analysis of the polymeric solids indicates thatthe relative concentration of carbazole and phthalimide functional unitsof thecopolymer are substantially the same as the gross mole compositionof the monomer charge. Molecular weight determinations were made bystandard vapor pressure osmometry techniques and indicate that thepolymeric product has a number average molecular weight of 100,000.

Additional polymeric compositions were prepared according to the abovetechnique from monomer charges containing one mole percent N-vinylphthalimide and 99 mole percent N- vinylcarbazole; 25 mole percentN-vinylphthalimide and percent N-vinylcarbazole; 50 mole percent N-vinylphthalimide and 50 mole percent N- vinylcarbazole; 75 percentN-vinylphthalimide and percent N-vinylcarbazole; and 99 percent N-vinylphthalimide and and one mole percent N- vinylcarbazole. Generally,the polymeric compositions thus prepared substantially reflected therelative concentration of the individual monomers in the charge. Otherphysical properties were also substantially the same as that reportedfor the above described composition.

The above polymeric products are subjected to spectral analysis on aCary 14R Spectrophotometer at room temperature. A series of solutionswere prepared from these polymeric products and homopolymers of poly-N-vinylcarbazole and poly-N-vinylphthalimide. Spectral grade methylenechloride was used as the solvent in all instances. All the copolymericmaterials exhibited a broad charge transfer band at 360 nanometers. Asimilar charge transfer band was not observed from a solution containinga mixture of the homopolymers. The most significant feature of thesespectra is the unusually high intensity of the charge transfer bandexhibited by these copolymer samples. This intensity is assumed to be afunction of the high concentration of the charge transfer complex insolution brought about by the forced interaction between adjacent donorand acceptor sites on the common polymeric backbone. This difference inelectronic properties is illustrated graphically by FIG. 3. Theintensity of this band remained unchanged even where solvents ofdifferent dielectric constants were used. All the evidence, thus,supports the assumption that this broad charge transfer band ispredominently attributable to a nondissociable intramolecularinteraction. That is to say that charge transfer interaction is takingplace predominently within the diads formed by adjacent donor andacceptor sites on common polymeric strands.

The above polymeric compositions can be formed into photoconductivefilms useful in electrophotography by simple solvent casting and coatingtechniques. For example, an imaging member useful in electrophotographycan be prepared from the polymeric compositions of this invention bydraw coating a 20 weight percent solution of one of the abovecompositions on an aluminized Mylar substrate. Typical of the solventswhich can be used as the vehicle in such a draw coating process aretetrahydrofuran and mixtures of toluenecyclohexanone (:60 by volume).The film thickness is controlled by adjustment of the viscosity of thecoating solution and/or by mechanical means. A photoconductive layerprepared as thus described should have a thickness in the range of fromabout 5 to about 50 microns in order to be suitable for use in anelectrophotographic imaging member. In addition to the aluminized Mylarsubstrate, any conductive substrate traditionally used inelectrophotography will provide a suitable ground plane for thephotoconductive imaging layer. In addition, a barrier layer may, ifdesired, be interfaced between the photoconductive layer and theconductor substrate in order to further reduce the rate of dark decay ofthe imaging member. Any of the organic or inorganic materials disclosedin Dessauer, US. Pat. No. 2,901,348 can be used as the material for thisbarrier layer.

In order to determine the relative photoconductive behavior of thevarious compositions of this invention, a series of electrophotographicimaging members are prepared as described above. The thickness of thephotoconductive imaging layer is about 15 microns. In addition toimaging members prepared from the various compositions of thisinvention, an additional imaging member is prepared from a homopolymerof poly-N- vinylcarbazole. In each instance, the imaging member iscorona charged in the dark to a positive potential of about 600 voltsand then exposed continuously to white light from a 200 watttungsteniodine lamp from a distance of 15 centimeters. In each instancethe time required to fully discharge the plate is noted. This experimentis repeated, except that the plate is now charged to a negativepotential of about 600 volts, the plate illuminated and the timerequired to completely discharge the surface potential also noted. Thedata collected indicates that the imaging member having aphotoconductive layer comprising about I mole percent structural unitsfrom N-vinylphthalimide and 99 mole percent structural units fromN-vinylcarbazole fully discharges a positive charge in about one-thirdthe time required to fully discharge a negative charge. The imagingmembers having a photoconductive layer comprising from about 10 to about50 mole percent structural units from N-vinylphthalimide are capable ofcomplete discharge of both positive and negative potentials insubstantially the same times. In all instances, the time required todischarge the imaging members having photoconductive layers preparedfrom the compositions of this invention were substantially less than thetime required to discharge the imaging member having a photoconductivelayer of poly-N- vinylcarbazole.

The imaging members are then further evaluated in order to determine theinitial rate of discharge of the photoconductive layer under continuouswhite light illumination. The result of this evaluation is summarized inthe Table presented below:

(Light source: continuous tungsten-iodine. L3 watts per squarecentimeter.)

Two of the imaging members previously tested are now further evaluatedwith regard to their photoresponse at different wavelengths. Forcomparison purposes, the action spectra of the imaging member having aphotoconductive layer of poly-N-vinylcarbazole has also been included.FIG. 1 provides the action spectrum for all three of these imagingmembers when placed under an applied positive potential. FIG. 2 providesa similar basis for comparison when these same imaging members are underan applied negative potential. The maximum photoresponse of all three ofthe compositions appears at a wavelength of about 3680 A; however, onlythe imaging members having photoconductive layers prepared from thecompositions of this invention tail off well into the visible portion ofthe spectrum. A comparison of FlGS. l and 2 would appear to indicatethat these two compositions operate fairly independent of the polarityof the applied potential. It is also apparent that the magnitude of thephotocurrent is related to the relative concentration the electron donorand electron acceptor moieties on the polymeric backbone. Maximumphotosensitivity is experienced when the copolymer composition comprisesabout 25 mole percent of structural units from N- vinylphthalimide andabout 75 mole percent of structural units from N-vinylcarbazole, andthus this copolymeric material is preferred.

In addition to the specific compositions discussed previously, a numberof isostructural modifications of the electron acceptor moiety of thecopolymer are possible without sacrifice of the photoconductivity of thecopolymer. In general, such modifications are made by effectingsubstitution of the electron acceptor moiety of the preformed polymericcomposition of this invention. This is achieved by quantative detachmentof the phthalimide group from the copolymer by subjecting the polymer tohydrazine. The equations which follow The photoconductivecharacteristics of films prepared from these polymeric products areevaluated on a Xerox Model D Copier equipped with a 100 Watt tungstenlamp (and shutter) located at a distance of 25 centimeters from thesurface of the film. The Model D is also outfitted with an electrometerand a potentiometric pen recorder for graphic documentation of thevoltage-time discharge behavior.

The examples which follow further define, describe and illustratepreparation and use of the polymeric compositions of this invention.Conditions and apparatus not specifically set forth in these specificembodiments are presumed to be standard or as hereinbefore described.Parts and percentages appearing in such examples are by weight unlessotherwise indicated.

EXAMPLE I Preparation of vinylamine/N-vinylcarbazo1e copolymer- 3.6grams of a random copolymer of N-vinylphthalimide/N-vinylcarbazole(9.2/90.8 mole percent) are dissolved in a solution containing 100milliliters of tetrahydrofuran and 10 milliliters of ethanol. After thecopolymer has been dissolved, 0.13 grams hydrazine are typical of suchisostructural modification. 25 hydrate (85 percent) are added and thesolution there- .3- L- "1.; r u

: l l 2 l V c. I

l NHZ l hydraz ine after heated to boiling under refluxing conditionsovernight. At the end of this interval, the solution apparently remainsunchanged, it retaining its characteristic yellow color. An additional2.6 grams of hydrazine hydrate are then added and the solution refluxedfor an additional two days. At the end of this time. the characteristicyellow color of the solution has disappeared and a white precipitateformed. The solution is now allowed to cool to room temperature and theprecipitate removed by filtration. This precipitate is believed to bephthalhydrazide. The polymer is separated from the solution byprecipitation with hexane in a Waring blender. The number averagemolecular weight of the polymeric product is about 78,000.

EXAMPLE II The procedure of Example I is repeated except for thesubstitution of a copolymer comprising about 25 mole percent structuralunits from N-vinylphthalimide and about 75 mole percent structural unitsfrom N- vinylcarbazole.

EXAMPLES III A series of copolymers are prepared by condensing the aminogroup of the vinylamine/N-vinylcarbazole copolymer withtetrahalophthalic anhydrides.

N-vinyltetrahalophthalimide/N-vinylcarbazole copolymers can be preparedby combining 0.45 grams of a copolymer comprisingvinylamine/N-vinylcarbazole (9.2/90.8 mole percent) and about 0.001 moleof tetrahalophthalic anhydride in 100 milliliters of cyclohexanone. Thissolution is prepared in a 250 milliliter flask equipped with a magneticstirring bar and reflux condenser. After the above ingredients aredissolved, a few drops of triethylamine catalyst are added to thesolution and the contents of the flask heated to boiling under refluxconditions. Heating continues for a period of about 2 days, after whichtime the colorless absorption will take on a yellow, yellow-orange,orange or light red color depending upon the anhydride in the solution.The solution is now allowed to cool to room temperature, and the polymerseparated by precipitation from methanol in a Waring blender. Where thepolymer forms a fine flocculent, separation may require centrifugation.The various isostructural modifications ofN-vinylphthalimide/N-vinylcarbazole exhibit maximum adsorption at about350 nanometers and tail off well into the visible band of the spectrum.

EXAMPLE IV Preparation of N-vinyl-2,4-dinitroaniline/N- vinylcarbazolecopolymer- 1 gram of a copolymer comprising vinylamine/N- vinylcarbazole(25/75 mole percent) is dissolved in 50 milliliters of anhydrousdimethylforamide (DMF). 0.184 grams potassium carbonate is thensuspended in this polymer solution and thereafter I milliliter of2,4-dinitrofluorobenzene (Sangers reagent) added by dropwise addition.Immediately after the addition of Sangers reagent a yellow colordevelops within the solution and becomes more intense as the reactionproceeds. The flask containing the solution is then heated over a steambath for about l V; hours at which time the polymer precipitated fromthe DMF by the addition of water. The precipitate is separated from thesolution by filtration and purified by washing with warm dilute aqueouspotassium hydroxide solution. This washing procedure is repeated severaltimes until the filtrate is colorless. The polymer is then dried in avacuum oven at about 70C. The number average molecular weight of theproduct is in the range of about 100,000.

EXAMPLE V Preparation of N-vinyl-4-nitroaniline/N- vinylcarbazolecopolymer about 1.5 grams of a polymer comprisingvinylamine/N-vinylcarbazole (/75 mole percent) is dissolved in 50milliliters of dimethyl formamide (DMF). The reaction vessel containingthis solution is purged of air with nitrogen and the remainder of thereaction carried out under this nitrogen blanket. About 0.27 gramspotassium carbonate is suspended in this solution and l thereafter onemilliliter of l-fluoro-4-nitrobenzene .added by dropwise addition. Theresulting mixture is heated over a steam bath for about 22 hours, thepolymer precipitated from the DMF by the addition of about 200milliliters of water. and the precipitate separated from the solution byfiltration. In order to assist in the separation of the polymer from thesolution, a small amount of ammonium chloride was added to assist incoagulation of the polymer. The isolated polymer is washed repeatedlywith dilute aqueous sodium hydroxide and then dried in a vacuum oven atabout C. The number average molecular weight of the polymericcomposition is in the range of about 93,000.

EXAMPLE VI The procedures of Example VI and V are repeated except forthe use of a copolymer comprising 9.2 mole percent structural units ofvinylamine and 90.8 mole percent structural units of N-vinylcarbazole.

A number of the polymeric compositions of the previous examples areevaluated with respect to their photoconductivity by first forming theminto an imaging layer on an aluminized Mylar substrate as previouslydescribed and then subjecting the resulting imaging member to standardelectrophotographic analysis.

Table ll which follows provides the results of such evaluation.

Table ll Initial potential d\'/dt Residual in volts in volts perpotential second per in volts micron of film thickness PolyN-vinyltetrachlorophthalimide/ N-vinylcarbazole 930 30 150 (25/75 mole71) 780 23 150 Poly N-vinyltetrabromophthalimide/ Nvinylcarbazole 10507.3 220 (ZS/75 mole 71) 680 1.9

Table ll Continued Initial potential dv/dt Residual in volts in voltsper potential second per in volts micron of film thickness PolyN-vinyltetraiodophthalimide/ N-vinylcarbazole 570 570 (25/75 mole /z)540 0 540 Poly N-vinyl-4-nitroaniline/N-vinylcarbazole 800 0 800 (25/75mole /r) Poly N-vinyl-ZA-dinitroaniline/Nninylcarbazole 540 6.4 I50(25/75 mole /1) 540 4.] 150 Poly N-vinylphthalimide/ N-vinylcarbazole1200 85 30 (25/75 mole 71) I300 65 30 Poly-vinylcarbazole 600 6.0 E00600 1.0 350 (Light source: continuous tungsten-iodine. 1.3 watts persquare cm.)

It, thus, appears that not all isostructural modifications of theN-vinylphthalimide/N-vinylcarbazole copolymer are photoconductive.Apparently the conformation of the modified materials as well as thesubtle electrical differences of the substituent groups tend to preventthe type of intramolecular charge transfer interaction exhibited bytheir photoconductive counterparts.

What is claimed is:

1. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer having structural units from (i) N-vinylcarbazole and (ii) N-vinylphthalimide.

2. The imaging member of claim 1 wherein the photoconductive filmcomprises a copolymer containing from about to about 50 mole percentstructural units from N-vinylphthalimide.

3. The imaging member of claim 1 wherein the photoconductive filmcomprises a copolymer containing from about to about 50 mole percentstructural units from N-vinylphthalimide.

4. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer having structural units from (i) N-vinylcarbazole and (ii) N-vinylphthalimide or the chloro-substitutedisostructural modifications thereof.

5. The imaging member of claim 4 wherein the polymeric photoconductivefilm comprises a copolymer containing from about 10 to about 50 molepercent structural units from N-vinylphthalimide or thechlorosubstituted isostructural modifications thereof.

6. The imaging member of claim 4 wherein the photoconductive filmcomprises a copolymer containing from about 25 to about 50 mole percentstructural units from N-vinylphthalimide or the chlorosubstitutedisostructural modifications thereof.

7. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer having structural units from (i) N-vinylcarbazole (ii) N-vinylphthalimide or the bromosubstitutedisostructural modifications thereof.

8. The imaging member of claim 7 wherein the photoconductive filmcomprises a copolymer containing from about 10 to about 50 mole percentstructural units from N-vinylphthalimide or the bromosubstitutedisostructural modifications thereof.

9. The imaging member of claim 7 wherein the photoconductive filmcomprises a copolymer containing from about 25 to about 50 mole percentstructural units from N-vinylphthalimide or the bromosubstitutedisostructural modifications thereof.

10. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer containing structural units from (i) N-vinylcarbazole and (ii) N-vinylphthalimide or the iodosubstitutedisostructural modifications thereof.

11. The imaging member of claim 10, wherein the photoconductive filmcomprises a copolymer containing from about 10 to about 50 mole percentstructural units from N-vinylphthalimide or the iodo-substitutedisostructural modifications thereof.

12. The imaging member of claim 10, wherein the photoconductive filmcomprises a copolymer containing from about '25 to about 50 mole percentstructural units from N-vinylphthalimide or the iodo-substitutedisostructural modifications thereof.

13. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer containing structural unites from (i)N-vinylcarbazole and (ii) a nitro-substituted N-vinylaniline.

14. The imaging member of claim 13 wherein the photoconductive filmcomprises a copolymer containing from about 10 to about 50 mole percentstructural units from a nitro-substituted N-vinylaniline.

15. The imaging member of claim 13 wherein the photoconductive filmcomprises a copolymer containing from about 25 to about 50 mole percentstructural units from a nitro-substituted N-vinylaniline.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,877,936

DATED April 15, 1975 INV ENTOR(S) William W. Limburg and Donald A.Seanor It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 2, line 12, change -or to "of" Column 2, line 15, change --p-- to"P".

Column 2, line 52, change preto "per Column 5, line 3, change and andto"and".

Column 6, line 8, change -tungsteniodineto "tungsten-iodine".

Column 9, lines 38-39, change -absorption-- to "solution".

Column 12, line 57, change -unites to "units".

Signed and Scaled this twenty-eight D ay Of October 1 975 [S AL] A nest:

RUTH C. MASON Arresting Officer

1. AN IMAGING MEMBER USEFUL IN ELECTROPHOTOGRAPHY COMPRISING ACONDUCTIVE SUBSTRATE AND OVERLYING AT LEAST ONE SURFACE OF SAIDSUBSTRATE A SUBSTANTIALLY CONTINUOUS POLYMERIC PHOTOCONDUCTIVE FILMCOMPRISING A COPOLYMER HAVING STRUCTURAL UNITS FROM (I) N-VINYLCARBAZOLEAND (II) NVINYLPHTHALIMIDE.
 2. The imaging member of claim 1 wherein thephotoconductive film comprises a copolymer containing from about 10 toabout 50 mole percent structural units from N-vinylphthalimide.
 3. Theimaging member of claim 1 wherein the photoconductive film comprises acopolymer containing from about 25 to about 50 mole percent structuralunits from N-vinylphthalimide.
 4. An imaging member useful inelectrophotography comprising a conductive substrate and overlying atleast one surface of said substrate a substantially continuous polymericphotoconductive film comprising a copolymer having structural units from(i) N-vinylcarbazole and (ii) N-vinylphthalimide or thechloro-substituted isostructural modifications thereof.
 5. The imagingmember of claim 4 wherein the polymeric photoconductive film comprises acopolymer containing from about 10 to about 50 mole percent structuralunits from N-vinylphthalimide or the chloro-substituted isostructuralmodifications thereof.
 6. The imaging member of claim 4 wherein thephotoconductive film comprises a copolymer containing from about 25 toabout 50 mole percent structural units from N-vinylphthalimide or thechloro-substituted isostructural modifications thereof.
 7. An imagingmember useful in electrophotography comprising a conductive substrateand overlying at least one surface of said substrate a substantiallycontinuous polymeric photoconductive film comprising a copolymer havingstructural units from (i) N-vinylcarbazole (ii) N-vinylphthalimide orthe bromo-substituted isostructural modifications thereof.
 8. Theimaging member of claim 7 wherein the photoconductive film comprises acopolymer containing from about 10 to about 50 mole percent structuralunits from N-vinylphthalimide or the bromo-substituted isostructuralmodifications thereof.
 9. The imaging member of claim 7 wherein thephotoconductive film comprises a copolymer containing from about 25 toabout 50 mole percent structural units from N-vinylphthalimide or thebromo-substituted isostructural modifications thereof.
 10. An imagingmember useful in electrophotography comprising a conductive substrateand overlying at least one surface of said substrate a substantiallycontinuous polymeric photoconductive film comprising a copolymercontaining structural units from (i) N-vinylcarbazole and (ii)N-vinylphthalimide or the iodo-substituted isostructural modificationsthereof.
 11. The imaging member of claim 10, wherein the photoconductivefilm comprises a copolymer containing from about 10 to about 50 molepercent structural units from N-vinylphthalimide or the iodo-substitutedisostructural modifications thereof.
 12. The imaging member of claim 10,wherein the photoconductive film comprises a copolymer containing fromabout 25 to about 50 mole percent structural units fromN-vinylphthalimide or the iodo-substituted isostructural modificationsthereof.
 13. An imaging member useful in electrophotography comprising aconductive substrate and overlying at least one surface of saidsubstrate a substantially continuous polymeric photoconductive filmcomprising a copolymer containing structural unites from (i)N-vinylcarbazole and (ii) a nitro-substituted N-vinyl-aniline.
 14. Theimaging member of claim 13 wherein the photoconductive film comprises acopolymer containing from about 10 to about 50 mole percent structuralunits from a nitro-substituted N-vinylaniline.
 15. The imaging member ofclaim 13 wherein the photoconductive film comprises a copolymercontaining from about 25 to about 50 mole percent structural units froma nitro-substituted N-vinylaniline.